1. Field of the Invention
The present invention relates to a tension mechanism in a power slide device for vehicle sliding door, and in particular, it relates to an improved tension roller for tension mechanism.
2. Description of the Related Art
In general, a conventional power slide device for vehicle sliding door comprises a wire drum rotated by motor, and a door-opening cable connected to the wire drum, and a door-closing cable connected to the wire drum. When the wire drum is rotated in a door-opening direction, the door-opening cable is wound up, and at the same time, the door-closing cable is pulled out, so that the sliding door is slid in the door-opening direction. On the contrary, when the wire drum is rotated in a door-closing direction, the door-opening cable is pulled out, and at the same time, the door-closing cable is wound up, so that the sliding door is slid in the door-closing direction.
The wire cable is retained at an appropriate tension by a tension mechanism. The tension mechanism comprises a pair of tension rollers biased in such a manner as to be adjacent to each other by elasticity of the springs.
FIG. 1 is a schematic view showing a relation among a wire drum A, a wire cable B, and a tension roller C. A typical thickness of the wire drum A along a drum shaft D is approximately 20 mm, and when the wire drum A rotates, the wire cable B is wound up (or pulled out), moving upward or downward guided by a helical engaging groove E of the wire drum A.
Since the typical tension roller C is a bobbin type roller with a short diameter in center, even if the wire cable B moves upward or downward in response to rotation of the wire drum A, the tension roller C substantially keeps the wire cable B at the center. The problem of this structure has been that the wire cable B is unmovable upward and downward relatively to the tension roller C. Hence, when the wire cable B moves upward or downward for the wire drum A, the wire cable B between the wire drum A and the tension roller C deviates widely from a right angle with the drum shaft D of the wire drum A, thereby often causing an engaging trouble between the wire cable B and the engaging groove E. The engaging trouble becomes serious as the distance between the wire drum A and the tension roller C becomes shorter. Consequently, the bobbin type tension roller C has been disposed at a place away from the wire drum A, thereby inviting a large size of the power slide device.
In contrast to this, as shown in FIG. 2, a tension roller C′ which is formed into a cylindrical roller having the same diameter from the top to the bottom is also publicly known. A cylindrical tension roller C′ attempts at miniaturization of the power slide device by forming the tension roller C′ at approximately 20 mm in accordance with the thickness of the wire drum A so that the space between the tension roller C′ and the wire drum A is made short.
The device of FIG. 2 has a problem in that a “cable rubbing noise” is generated when the wire drum A is rotated. A cause of the noise generation will be described below.
By the rotation of the wire drum A, when the cable B, for example, moves upward for the wire drum A, the upward movement of the cable B relatively to the tension roller C′ is slightly delayed. Hence, an angle X between the cable B and the lower side surface of the roller C′ exceeds more than 90 degrees. Then, a downward external force as shown by an arrow a is applied to the cable B in the vicinity of the roller C′ so that the upward movement of the cable B in the vicinity of the roller C′ is further delayed. As a result, the wire cable B rubs against an angular portion of the engaging groove E of the wire drum A, thereby generating the noise.
Further, the cable B in the vicinity of the roller C′ abruptly moves in order to catch up on the delay of the upward movement, thereby causing the noise.